Renewable energy systems, such as wind turbine systems, solar power systems, etc., have increasingly been used for power generation throughout the world. Renewable energy power systems, such as wind energy power systems and solar energy power systems, can include a power converter configured to convert energy generated by the renewable energy source (e.g. a wind-driven generator, a photovoltaic array, etc.) into suitable energy for application to an AC grid.
Energy storage systems, such as battery energy storage systems, have been used in conjunction with renewable energy systems to reduce transients in energy produced by the renewable energy systems due to, for instance, varying wind conditions, varying sunlight conditions, etc. For instance, during periods of increased energy production resulting from increased wind conditions, the extra energy produced by the renewable energy source can be stored in the energy storage system, for instance, by charging batteries in the energy storage system. During periods of decreased energy production resulting from decreased wind conditions, the energy storage system can be used to supplement the energy produced by the renewable energy source, for instance, by discharging batteries in the energy storage system.
Control schemes for controlling a state of charge of an energy storage system in conjunction with the renewable energy system typically do not store energy up to a maximum available capacity (e.g. maximum state of charge) of the energy storage devices. Typically, control schemes are set up to operate the renewable energy system so that it can deliver a constant amount of energy for short durations of time. The energy storage devices can be maintained at a state of charge level that is less than then the maximum state of charge. In this way, the energy storage devices can be operated to either absorb or deliver energy as necessary to keep the output of the renewable energy system relatively constant. In some circumstances, however, there is not enough stored energy in the energy storage devices to accommodate what is needed to support the desired output power of the renewable energy system.
Thus, a need exists for a control scheme for controlling the state of charge of the energy storage system to increase the capability of the energy storage system to support energy requirements of the renewable energy system.